[vsnet-grb-info 27954] GRB 210517A: KCT optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30057
SUBJECT: GRB 210517A: KCT optical upper limit
DATE:    21/05/20 06:11:09 GMT
FROM:    Gregory SungHak Paek at SNU  <shpaek at astro.snu.ac.kr>

Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Gu Lim (SNU
ARC/SNU), on behalf of GECKO collaboration

 We searched for the optical counterpart of GRB 210517A (V. E'Elia et al.
GCN #30032) with the 0.36-m class KCT (KIAS Chamnun Telescope) in
DeepSkyChile, one of the facilities of the GW EM-Counterpart Korean
Observatory (GECKO).

 We observed the center of Swift/XRT localization (RA, Dec = 358.2245
-39.1020) +2.94 hours after report, but could not find any possible
transient within the field of view and at the reported location of optical
afterglow (N. R. Tanvir et al. GCN 30037). We calibrated flux with the
APASS catalog and used an AB magnitude system. Depth means 5 sigma upper
limit for a point source detection. The magnitudes are not corrected for
galactic extinction.

------
Filter Date-obs[UT] Exp.time[s] Depth
I 2021-05-17T08:24:35.583 180*3 18.435
R 2021-05-17T08:37:00.750 180*3 19.581
V 2021-05-17T08:49:25.333 180*3 20.005
B 2021-05-17T09:01:50.250 180*3 20.047

Gravitational-wave EM Counterpart Korean Observatory (GECKO) is a network
of 10+ 0.5m to 1m class telescopes over the world.